<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .pink{
            background-color: pink;
        }
    </style>
</head>
<body>
    <button class = 'pink'>测试按钮1</button>
    <button>测试按钮2</button>
    <button>测试按钮3</button>

    <script>
        var btns = document.querySelectorAll('button');
        for (var i = 0; i < btns.length; i++) {
            btns[i].addEventListener('click',function(){
                document.querySelector('.pink').classList.remove('pink');
                this.classList.add('pink');
            })
        }
    </script>
</body>
</html>